Jitter detection device and image quality correction device for adaptively changing correction when reproducing video signal

ABSTRACT

A jitter detection device for detecting jitter of a video signal (Sv) measures a vertical period (Stf(v)) of one field (v) of the video signal (Sv) to determine, based on a vertical period signal (Stf(v)), whether the video signal (Sv) jitters or not. If the number of times (Cej) it is successively determined that the video signal (Sv) jitters is smaller than a first predetermined number of times (Tej), the video signal (Sv) is confirmed to be a jitter signal (Svj). If the number of times (Cnj) it is successively determined that the video signal (Sv) does not jitter is smaller than a second predetermined number of times (Cnj), the video signal (Sv) is confirmed to be a non-jitter signal (Svjn).

TECHNICAL FIELD

This invention relates to image quality correction devices that carryout a variety of processes on an image signal to correct quality of animage reproduced based on the image signal and, more specifically, to animage quality correction device that corrects the image quality with anappropriate amount of correction according to an amount of jitter in avideo signal that greatly affects the image quality.

BACKGROUND ART

FIG. 22 is a conventional image correction device used for an analogvideo signal Sv, based on which an image is displayed on an imagedisplay device used in a television set typified by an LCD or CRT. Asshown in the drawing, a signal processing system SPc in the televisionset carries out a variety of processes on the video signal Sv, andgenerates signals required for displaying images on an image displaydevice 9 (in the present example, CRT), that is, a scan speed modulationsignal VSCc, an image signal Si, and a horizontal synchronization signalHsync, and a vertical synchronization signal Vsync, each carryinginformation according to the characteristics of the image display device9.

Based on the scan speed modulation signal VSCc, a scan speed modulationdriver 6 carries out scanning at a predetermined speed, and generates animage quality correction scan drive signal Sscd to correct the qualityof the image displayed on the image display device 9. Based on the imagesignal Si, a CRT driver 7 generates a CRT drive signal Scrtd for makingthe image display device 9 display an image. Based on synchronizationsignals Ssync, the deflector 8 generates a deflection drive signal Sdfdfor making the image display device 9 operate with a predeterminedamount of deflection and carry out raster scanning. The image displaydevice 9 is driven by these drive signals Sscd, Scrtd, and Sdfd todisplay the image carried by the video signal Sv.

The signal processing system SPc includes a sync separator 4, an imagequality correction device IQCc, and a signal processor 5. The syncseparator 4 extracts the horizontal synchronization signal Hsync and thevertical synchronization signal Vsync from the video signal Sv.

Based on the horizontal synchronization signal Hsync and the verticalsynchronization signal Vsync, the image quality correction device IQCcperforms image quality correction processing on the video signal Sv, andgenerates an image-quality-corrected video signal SIQc, and alsogenerates the scan speed modulation signal VSCc. Based on theimage-quality corrected video signal SIQc, the signal processor 5generates the image signal Si. Note that the operation of the signalprocessing system SPc is controlled by a controller 100 c.

The image quality correction device IQCc includes a scan speedmodulation signal generator 11 for defining a scan speed for the imagedisplay device 9, a horizontal edge enhancer 12 for defining an amountof horizontal edge enhancement for the image signal Si, a noise reducer(NR) 13 for reducing noise components included in the image signal Si, amultiplexer 14, a bus interface 15, and ROM 16.

Based on the horizontal synchronization signal Hsync, the verticalsynchronization signal Vsync, and the video signal Sv, the scan speedmodulation signal generator 11 determines a raster scan speed VSC (notshown) that corresponds to the image signal Si. Similarly, based on thehorizontal synchronization signal Hsync, the vertical synchronizationsignal Vsync, and the video signal Sv, the horizontal edge enhancer 12determines an amount of horizontal edge enhancement OE (not shown) ofthe video signal Sv.

Even if the video signal Sv is uniform in quality, the video carried bythe video signal Sv and displayed on the image display device 9 isaffected by physical characteristics of the television set including theimage display device 9; a drive circuit system such as the scan speedmodulation driver 6, the CRT driver 7, and the deflector 8; and a signalprocessing system. Therefore, the above-stated scan speed VSC and amountof horizontal edge enhancement OE cannot be uniquely determined based onthe horizontal synchronization signal Hsync, the verticalsynchronization signal Vsync, and the video signal Sv. For this reason,depending on the physical characteristics of the television set wherethe image quality correction device IQCc is used, each predeterminedamount of correction is calculated in advance for a correcting operationof each of the scan speed modulation signal generator 11, the horizontaledge enhancer 12 and the NR 13.

Then, predetermined amounts of correction SCAc are stored in the ROM 16.When the quality of the image carried by the video signal Sv iscorrected by the image quality correction device IQCc, the predeterminedamounts of correction SCAc are read from the ROM 16 thorough a businterface 15, and supplied to the scan speed modulation signal generator11, the horizontal edge enhancer 12, and the NR 13 for correcting eachoperation.

Specifically, the predetermined amounts of correction SCAc include acorrection amount of scan speed SVMc that is predetermined for the scanspeed VSC defined by the scan speed modulation signal generator 11; acorrection amount of horizontal edge enhancement SOEc that ispredetermined for the amount of horizontal edge enhancement OE definedby the horizontal edge enhancer 12; and a correction amount of noisereduction SNRc that is predetermined for the amount of noise reductionby the NR 13.

As such, the horizontal edge enhancer 12 determines the amount ofhorizontal edge enhancement OE of the video signal SV based on thecorrection amount of horizontal edge enhancement SOEc supplied by theROM 16 via the bus interface 15, and generates ahorizontal-edge-enhancement-corrected signal OEc. The multiplexer 14multiplexes the video signal Sv with thehorizontal-edge-enhancement-corrected signal OEc, and generates ahorizontal-edge-enhanced-corrected signal VOEc, which is the videosignal Sv enhanced in horizontal edge by the amount of horizontal edgeenhancement OE.

In a similar manner to that of the horizontal edge enhancer 12, the NR13 reduces noise of the horizontal-edge-enhanced video signal VOEc, andgenerates the image-quality-corrected video signal SIQc, based on noisereduction characteristics corrected with the correction amount of noisereduction SNRc supplied by the ROM 16 through the bus interface 15.

The image processor 5 generates the image signal Si based on theimage-quality-corrected video signal SIQc.

As described above, in the conventional image quality correction deviceIQCc, the video signal Sv is corrected in scan speed modulation,horizontal edge amount, and noise reduction for each predeterminedamount, considering effects of the physical characteristics of thetelevision set and other factors. In other words, the amount correctedby the image quality correction device IQCc is always constantirrespectively of change in quality of the video signal Sv.

However, the quality of the video signal Sv changes with time. If thevideo signal Sv jitters, the image-quality-corrected video signal SIQCand scan speed modulation signal VSCc outputted from the image qualitycorrection device IQCc also jitter. Therefore, based on these jitteringimage-quality-corrected video signal SIQc and the scan speed modulationsignal VSCc, the amount of jitter in video reproduced by the videodisplay device 9 is increased, thereby deteriorating the reproducedvideo in quality.

For example, if the video signal Sv having jitter is subjected tohorizontal edge enhancement for greatly enhancing the edge, glare at anedge part is enhanced by jitter in the horizontal edge enhancementsignal itself. Thus, the jitter in the reproduced image is enhanced bythe image quality correction processing. To prevent this, the amount ofimage quality correction for edge enhancement is reduced, while the onefor noise reduction is increased.

In other words, to prevent video image quality deterioration or toimprove video image quality resulting from the quality (jitter) of thevideo signal Sv, each correction by the scan speed modulation signalgenerator 11, the horizontal edge enhancer 12, and the NR 13 is adjustedaccording to the amount of jitter in the video signal Sv. That is, ifthe video signal Sv jitters, corrections by the scan speed modulationsignal generator 11 and the horizontal edge enhancer 12 are suppressed,while the one by the NR 13 is promoted.

For this purpose, the presence or absence of jitter of the video signalSv and the amount of jitter have to be accurately detected.Conventionally, however, means for accurately detecting the presence orabsence of jitter of the input video signal Sv and the amount of jitteris not provided as being incorporated in an image display device such asa television set.

DISCLOSURE OF THE INVENTION

To solve the above problems, a first aspect of the present invention isa jitter detection device for detecting jitter in a video signal,comprising:

a vertical period measuring unit for measuring a vertical period for onefield of the video signal and generating a vertical period signal;

a jitter determination unit for determining, based on the verticalperiod signal, whether the video signal jitters or not, and generating ajitter determination signal;

a jitter determination counter for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal jitters, and generating a jitter determinationcounter signal;

a jitter confirmation unit for confirming, based on the jitterdetermination counter signal, that the video signal is a jitter signalif it is determined a first predetermined number of times that the videosignal jitters;

a non-jitter counting unit for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal does not jitter, and generating a non-jitterdetermination counter signal;

a non-jitter confirmation unit for confirming, based on the non-jitterdetermination counter signal, that the video signal is a non-jittersignal if it is determined a second predetermined number of times thatthe video signal does not jitter.

As described above, in the first aspect, the state and the jitter amountof the video signal can be accurately detected while eliminating theeffects of disturbance factors such as noise components of the videosignal or a television set side.

According to a second aspect, in the first aspect, the jitterdetermination unit:

determines that the video signal jitters when an absolute value of adifference between a vertical period of a present field and a verticalperiod of a previous field Stf is larger than 1; and

determines that the video signal does not jitter when the absolute valueis smaller than 1.

A fourth aspect is directed to an image quality correction device forcorrecting quality of an image reproduced based on a video signalaccording to an amount of jitter in the video signal, further includingan image quality correction adjuster that comprises at least one of:

a noise reduction unit for reducing noise of the video signal based on apredetermined correction amount of noise reduction;

a horizontal edge enhancer for enhancing a horizontal edge of the videosignal based on a predetermined correction amount of horizontal edgeenhancement; and

a scan speed modulator for enhancing a specific part of the video signalbased on a predetermined amount of scan speed modulation, wherein:

according to the amount of jitter, the correction amount of noisereduction is increased by a predetermined adjustment value, thecorrection amount of horizontal edge enhancement is decreased by theadjustment value, and the amount of scan speed modulation is decreasedby the adjustment value.

As described above, in the fourth aspect, image quality can be correctedwith appropriate adjustment according to the state of jitter of thevideo signal.

According to a fifth aspect, in the fourth aspect, the image qualitycorrection device further comprises a jitter detection device thatcomprises:

a vertical period measuring unit for measuring a vertical period for onefield of the video signal and generating a vertical period signal;

a jitter determination unit for determining, based on the verticalperiod signal, whether the video signal jitters or not, and generating ajitter determination signal;

a jitter determination counter for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal jitters, and generating a jitter determinationcounter signal;

a jitter confirmation unit for confirming, based on the jitterdetermination counter signal, that the video signal is a jitter signalif it is determined a first predetermined number of times that the videosignal jitters;

a non-jitter counting unit for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal does not jitter, and generating a non-jitterdetermination counter signal;

a non-jitter confirmation unit for confirming, based on the non-jitterdetermination counter signal, that the video signal is a non-jittersignal if it is determined a second predetermined number of times thatthe video signal does not jitter.

According to a sixth aspect, in the fifth aspect, the image qualitycorrection adjuster dynamically adjusts at least one of the correctionamount of noise reduction, the correction amount of horizontal edgeenhancement, and the amount of scan speed modulation, while sequentiallycalculating a dispersion value of vertical periods.

According to a seventh aspect, in the sixth aspect, the image qualitycorrection adjuster further comprises a histogram unit for generating ahistogram composed of a frequency of appearance with respect to theamount of jitter, wherein:

at least one of the correction amount of noise reduction, the correctionamount of horizontal edge enhancement, and the amount of scan speedmodulation is adjusted by an amount of adjustment predeterminedcorresponding to the amount of jitter and the frequency of appearancethat is larger than a predetermined threshold.

According to an eighth aspect, in the fourth aspect, the amount ofjitter in a present field is used as the adjustment value immediatelyafter the video signal is changed from a non-jitter signal to a jittersignal.

According to a ninth aspect, in the fifth aspect, the image qualitycorrection device comprises an adjustment suppressor for suspendingadjustment of at least one of the correction amount of noise reduction,the correction amount of horizontal edge enhancement, and the amount ofscan speed modulation if the video signal is changed from the jittersignal to the non-jitter signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an image qualitycorrection device used in a television set, according to the presentinvention.

FIG. 2 is a block diagram showing the structure of a correction adjustershown in FIG. 1.

FIG. 3 is a flow chart showing the main operation of the correctionadjuster shown in FIG. 2.

FIG. 4 is a flow chart showing the detailed operation of a verticalaverage period calculation subroutine shown in FIG. 3.

FIG. 5 is a flow chart showing the detailed operation of a jitterconfirmation subroutine shown in FIG. 3.

FIG. 6 is a flow chart showing the detailed operation of a non-jitterconfirmation subroutine shown in FIG. 3.

FIG. 7 is a flow chart showing the detailed operation of a jitter amountcalculation subroutine shown in FIG. 3.

FIG. 8 is a flow chart showing the detailed operation of an adjustmentamount of image quality correction calculation subroutine shown in FIG.3.

FIG. 9 is a diagram demonstrating characteristic amounts of a non-jittersignal.

FIG. 10 is a diagram demonstrating characteristic amounts of a jittersignal.

FIG. 11 is a diagram demonstrating a method for adjusting a slope of apredetermined amount of correction according to the amount of jitter.

FIG. 12 is a diagram demonstrating a method for adjusting thepredetermined amount of correction by uniformly increasing or decreasingthe amount.

FIG. 13 is a diagram demonstrating an image quality correction amountcalculation subroutine shown in FIG. 3.

FIG. 14 is a diagram demonstrating an image quality correction parametergeneration subroutine shown in FIG. 3.

FIG. 15 is a flow chart showing the main operation of a correctionadjuster according to one exemplary modification of the embodiment ofthe present invention.

FIG. 16 is a flow chart showing the detailed operation of a jitterconfirmation subroutine shown in FIG. 15.

FIG. 17 is a flow chart showing the detailed operation of a non-jitterconfirmation subroutine shown in FIG. 15.

FIG. 18 is a first half of a flow chart showing the detailed operationof a jitter amount calculation/image quality correction amountcalculation subroutine shown in FIG. 15.

FIG. 19 is a second half of the flow chart showing the detailedoperation of the jitter amount calculation/image quality correctionamount calculation subroutine shown in FIG. 15.

FIG. 20 is a diagram demonstrating the jitter amount calculation/imagequality correction amount calculation subroutine shown in FIG. 15.

FIG. 21 is another diagram demonstrating the jitter amountcalculation/image quality correction amount calculation subroutine shownin FIG. 15.

FIG. 22 is a block diagram showing the structure of a conventional imagequality correction device used in a television set.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, the present invention is described infurther detail.

First, with reference to FIGS. 1 through 14, an image quality correctiondevice according to one embodiment of the present invention isdescribed. Then, with reference to FIGS. 15 through 21, one exemplarymodification of the image quality device according to the embodiment ofthe present invention is described in detail.

Prior to providing a specific description of the present embodiment, abasic concept of the image quality correction device according thepresent invention is first described. As stated above, in the imagedisplay device typified by a television set, quality of an imagedisplayed on an image display device is generally affected by thequality of a video signal and physical characteristics of the televisionset. The quality of the video signal depends on jitter or noise, and thephysical characteristics of the television set depend on a jitterresponse and frequency characteristics of a signal processing system,and a focus performance and gamma characteristics of the image displaydevice.

In general, to improve the quality of the image displayed on the imagedisplay device, the processing includes horizontal edge enhancement withrespect to a video signal, raster scan speed modulation with respect tochanges of a luminance signal in the image display device (hereinafterreferred to as “scan speed modulation”), and noise reduction processingfor reducing the effects of noise components in the video signal. For ajittering video signal, horizontal edge enhancement and scan speedmodulation cause further deterioration in quality of the reproducedimage, and therefore have to be suppressed. Noise reduction, on theother hand, improves the reproduced image, and therefore does not haveto be suppressed.

In other words, as the amount of jitter in the video signal increases,horizontal edge enhancement and high scan speed modulation aresuppressed, while noise reduction is promoted. As the amount of jitterin the video signal decreases, horizontal edge enhancement and scanspeed modulation are promoted, while noise reduction is decreased. Assuch, in the present invention, horizontal edge enhancement, scan speedmodulation, and the noise reduction amount are appropriately adjustedaccording to the amount of jitter in the video signal, thereby ensuringthe quality of the image reproduced by the image display device.(Embodiment)

Shown in FIG. 1 is a state where the image quality correction deviceaccording to one embodiment of the present invention is used in atelevision set typified by an LCD or CRT. As shown in the drawing, inthe television set, a signal processing system SPp carries out a varietyof processes on a video signal Sv for generating a raster scan speedmodulation signal VSCv, an image signal Si, and a horizontalsynchronization signal Hsyn, and a vertical synchronization signalVsync, each carrying information according to the characteristics of animage display device 9 and required for displaying an image on the imagedisplay device 9 (in the present example, CRT).

Based on the scan speed modulation signal VSCv, a scan speed modulationdriver 6 changes a raster scan speed with a second-derivative signalindicating changes in luminance of the video signal Sv, and generates ascan drive signal Sscd for correcting the quality of the image displayedon the image display device 9. Based on the image signal Si, a CRTdriver 7 generates a CRT drive signal Scrtd for making the image displaydevice 9 display the image. A deflector 8 generates a deflection drivesignal Sdfd for making the image display device 9 operate at apredetermined angle of deflection. Driven by these drive signals Sscd,Scrtd, and Sdfd, the image display device 9 displays the image carriedby the video signal Sv.

The signal processing system SPp includes a sync separator 4, an imagequality correction device IQCp, and a signal processor 5. The syncseparator 4 extracts the horizontal synchronization signal Hsync and thevertical synchronization signal Vsync from the video signal Sv.

Based on the horizontal synchronization signal Hsync and the verticalsynchronization signal Vsync, the image quality correction device IQCpcarries out image quality correction processing on the video signal Sv,and generates an image-quality-corrected video signal SIQv and also ascan speed modulation signal VSCv. Based on the image-quality-correctedvideo signal SIQv, the signal processor 5 generates the image signal Si.Note that the operation of the signal processing system SPp iscontrolled by a controller 100 p. Each component of the signalprocessing system SPp generates a signal indicating a state of its own,and outputs the signal as a state signal Sr to the controller 100 p.Based on the received state signal Sr, the controller 100 p recognizesthe state of each component, and produces a control signal Sc forcontrolling the operation of each component.

The image quality correction device IQCp includes a scan speedmodulation signal generator 11 for defining a scan speed VSC for theimage display device 9, a horizontal edge enhancer 12 for defining anamount of horizontal edge enhancement for the image signal Si, a noisereducer (NR) 13, a multiplexer 14, a bus interface 15, a ROM 16, and acorrection adjuster CA.

Stored in the ROM 16 are predetermined amounts of correction SCAcpredetermined according to the physical characteristics of thetelevision set used in the image quality correction device IQCp forcorrecting each function of the scan speed modulation signal generator11, the horizontal edge enhancer 12, and the NR 13. The reason is that,even though the video signal Sv is uniform in quality, the video carriedby the video signal Sv is displayed on the image display device 9 asbeing affected by the physical characteristics and other factors of thetelevision set including the image display device 9; a drive circuitsystem such as the scan speed modulation driver 6, the CRT driver 7, andthe deflector 8; and a signal processing system. For this reason, theseamounts of correction are provided to compensate the effects of thephysical characteristics of the television and other factors, based onthe predetermined amounts of correction SCAc for the scan speed VSC, theamount of horizontal edge enhancement OE, and an amount of noisereduction NR that are all determined in advance.

The correction adjuster CA measures, based on the verticalsynchronization signal Vsync extracted from the sync separator 4, theamount of jitter in the video signal Sv, and calculates, according tothe measured jitter, each appropriate amount of correction by the signalgenerator 11, the horizontal edge enhancer 12, and the NR 13. Then,based on each appropriate amounts of correction, the predeterminedamounts of correction SCAc read from the ROM 16 are adjusted, andappropriate amounts of correction SCAv are generated.

Specifically, the appropriate amounts of correction SCAv include anappropriate correction amount of scan speed SVMv for adjusting apredetermined amount of correction SVM of the scan speed VSC determinedby the scan speed modulation signal generator 11; an appropriatecorrection amount of horizontal edge enhancement SOEv for adjusting theamount of horizontal edge enhancement OE determined by the horizontaledge enhancer 12; and an appropriate correction amount of noisereduction SNRv for adjusting a predetermined value SNR for adjusting theamount of noise reduction in the NR 13. Each appropriate amount ofcorrection SCAv is supplied via the bus interface 15 to the speedmodulation generator 11, the horizontal edge enhancer 12, and the NR 13for correcting each operation.

Based on the horizontal synchronization signal Hsync, the verticalsynchronization signal Vsync, the video signal Sv and the appropriatecorrection amount of scan speed SVMv, the scan speed modulation signalgenerator 11 determines the raster scan speed VSc of the image displaydevice 9, and generates an appropriate scan speed modulation signalVSCv.

Similarly, based on the horizontal synchronization signal Hsync, thevertical synchronization signal Vsync, the video signal Sv and theappropriate correction amount of horizontal edge enhancement SOEv, thehorizontal edge enhancer 12 determines the amount of horizontal edgeenhancement OEv of the video signal Sv, and generates an appropriatecorrected horizontal edge enhancement signal OEv.

The multiplexer 14 multiplexes the video signal Sv and the appropriatecorrected horizontal edge enhancement signal OEv together, andgenerates, for output to the NR 13, an appropriatehorizontal-edge-enhanced video signal VOEv, in which horizontal edgecomponents of the video signal Sv are enhanced by an amount indicated bythe appropriate corrected horizontal edge enhancement signal OEv.

The NR 13 reduces noise components in the appropriatehorizontal-edge-enhanced video signal VOEv, and generates animage-quality-corrected video signal SIQv. This generation is carriedout in a similar manner to that of the horizontal edge enhancer 12,based on the noise reduction characteristics after correction indicatingthe appropriate correction amount of noise reduction SNRv supplied bythe correction adjuster CA via the bus interface 15.

The signal processor 5 generates the image signal Si based on theimage-quality corrected video signal SIQv. In this fashion, the amountof jitter detected by the correction adjuster CA based on the verticalsynchronization signal Vsync is referred to for optimizing the amountsof correction. With these amounts of correction, horizontal edgeenhancement, noise reduction, and modulation of the raster scan speed ofthe image display device 9 are carried out, and an image is reproducedon the image display device 9 with high quality.

With reference to FIG. 2, the structure and operation of the correctionadjuster CA are described below. As shown in FIG. 2, the correctionadjuster CA includes a vertical period measuring unit 21, a jitterdetector 22, a jitter amount measuring unit 23, and an image qualitycorrection amount calculator 24.

The vertical period measuring unit 21 measures, based on the verticalsynchronization signal Vsync provided by the sync separator 4, avertical period of a present field v of the video signal Sv, andgenerates a vertical period signal Stf(v).

The jitter detector 22 determines, based on the vertical period signalStf(v) supplied by the vertical period measuring unit 21, whether thevideo signal Sv is a jitter signal Sv or a non-jitter signal Svjn, andgenerates a jitter detection signal Sjd, and also a jitter transitionsignal Sff indicating that the video signal Sv is changed from thejitter signal Svj to the jitter signal Svj and vice versa.

The jitter amount measuring unit 23 detects, based on the verticalperiod signal Stf(v) supplied by the vertical period measuring unit 21,the amount of jitter in the video signal Sv to generate a jitter amountsignal Sdsp.

The image quality correction amount calculator 24 calculates, based onthe jitter detection signal Sjd supplied by the jitter detector 22 andthe jitter amount signal Sdsp supplied by the jitter amount measuringunit 23, each appropriate amount of correction for the scan speedmodulation signal generator 11, the horizontal edge enhancer 12, and theNR 13 according to the amount of jitter in the video signal Sv. Theimage quality correction amount calculator 24 then adjusts thepredetermined amounts of correction SCAc read from the ROM 16 togenerate the appropriate amounts of correction SCAv (SVMv, SOEv, andSNR). Needless to say, the correction adjuster CA may be structured by aCPU. Note that, the vertical period Stf(v) may be obtained every severalfields if it cannot be obtained every field due to the processingcapabilities of the CPU.

With reference to FIGS. 9 and 10, characteristic amounts for making adetermination of jitter/non-jitter of the video signal Sv are described.Shown in FIG. 9 are characteristic amounts of the video signal Sv thatdo not jitter, that is, non-jitter signal Svjn. In the drawing, a fieldV is shown in the left column, each field's vertical period is shown inthe center column, and an inter-field vertical period differenceΔStf(v). The vertical period Stf(V) is a difference between a previousfield's vertical period Stf(V−1) and a present field's vertical periodStf(V).

As shown in the drawing, in the non-jitter signal Svjin, the inter-fieldvertical period difference ΔStf(V) is within a range of −1, 0, and 1,where the field V=0 to n−1 (arbitrary positive integer). Such non-jittersignal Svjn is called a standard signal, in which the frequency of acolor burst signal synchronizes with the horizontal and verticalfrequencies.

If the horizontal and vertical frequencies are measured at a clock fourtimes (4Fsc) that of the color burst signal, the horizontal frequency is910 CLK, and the vertical frequency is 910 CLK×262.5=238875. Thesevalues are represented in hexadecimal as 38 e horizontal counter valuefor the horizontal frequency, and 3 a 51 b vertical counter value forthe vertical frequency. In the present embodiment, the clock used formeasuring the vertical period is a 4Fsc clock that is locked to burstbut not locked horizontally. Therefore, a measurement error of ±1 CLK orless may occur. For this reason, the difference from the previousfield's vertical period Stf(V), that is, the inter-field vertical perioddifference ΔStf(V) becomes ±2 CLK or less.

However, there is a near-zero probability that the inter-field verticalperiod difference ΔStf(V) actually becomes ±2 CLK, because thehorizontal synchronization signal Hsync and the vertical synchronizationsignal Vsync are counted down from the stable burst signal. Based onthat fact, the video signal Sv is determined as the non-jitter signalSvjn if the inter-field vertical period difference ΔStf(V) becomes ±1 orless. Besides the standard signal, a signal whose horizontal andvertical frequencies are constant can also be regarded as the standardsignal (non-jitter signal Svjn).

Shown in FIG. 10 are characteristic amounts of the video signal Sv thatjitters, that is, the jitter signal Svj. Unlike the case of thenon-jitter signal Svjn shown in FIG. 9, in the jitter signal Svj, theinter-field vertical period difference ΔStf(V) varies within a rangebetween −15 and 16, where the field V=0 to n−1. The jitter signal Svjis, for example, a video signal outputted from an analog video taperecorder. In this case, the structure of the analog video tape recordermakes it very difficult to completely eliminate jitter from an outputvideo signal.

As shown in FIG. 10, in the jitter signal Svj, frequencies betweenfields V vary continuously. If an amount of variation dsp is measured,for example, if dispersion is calculated, the amount of jitter can becorrectly detected. The amount of jitter should be measured at ahorizontal rate, because adjusting the amount of image qualitycorrection means correcting horizontal image quality. However, somedifficulties occur as typically listed below.

First, the period has to be measured at a considerably high clock. Next,the amount of calculation is enormous. Furthermore, since the horizontalfrequency is short, it is extremely difficult to ensure measurementaccuracy.

In consideration of such difficulties, in the present invention, jitteris measured based on a vertical amount of jitter as a result ofintegrating jitter components of the jitter signal Svj. If jitter ismeasured based on the vertical amount of jitter, however, there is aconcern that jitter is cancelled out when the vertical amounts of jitterare integrated or when the present field and the previous field have thesame period.

In fact, however, in analog video tape recorders, there is a near-zeropossibility that the present field and the previous field become thesame in frequency. Also, there is a fact that the difference in theamount of jitter from the previous field becomes large when the amountof jitter is large. Based on these facts, in the present invention,jitter can be accurately measured based on the vertical amount ofjitter. With reference to FIGS. 3 to 7, a method of measuring jitter isspecifically described.

With reference to a main flow chart shown in FIG. 3, the main operationof the correction adjuster according to the embodiment of the presentinvention is described. When the television set equipped with the imagequality correction device IQCp is started to operate, in step #100, thecorrection adjuster CA is initialized. In other word, a jitterconfirmation flag ex_jitter corresponding to the jitter detection signalSjd generated by the jitter detector 22 is set to 0; first_flagcorresponding to the jitter transition signal Sff is set to 1; the fieldv, which is a variable corresponding to the present field V, is set to0; and the amount of jitter dsp, which is a variable corresponding tothe jitter amount signal Dsp, is set to 0.

The jitter confirmation flag ex_jitter 0 indicates that the video signalSv is the non-jitter signal Svjn, while 1 indicates that the videosignal Sv is the jitter signal Svj. The first_flag 0 indicates thatcorrection adjustment is successively carried out on the same videosignal, while 1 indicates that correction adjustment has not yet startedon the same video signal Sv.

As such, the video signal Sv is handled as not jittering when the imagequality correction device IQCp (correction adjuster CA) starts tooperate. Therefore, as a matter of course, image quality correctionadjustment has not started (first_flag=1). The procedure then goes tostep #200.

In step #200, a vertical average period calculation subroutine forcalculating the vertical period of the video signal is executed. Thevertical average period calculation subroutine is executed by thevertical period measuring unit 21, and will be described in detail belowwith reference to FIG. 4. The procedure then goes to step #700.

In step #700, the amount of jitter in the video signal Sv is calculated.The jitter amount calculation subroutine in this step is executed by thejitter amount measuring unit 23, and will be described in detail belowwith reference to FIG. 7. The procedure then goes to step #300.

In step #300, it is determined whether or not the jitter confirmationflag ex_jitter is 1, that is, whether the video signal Sv is the jittersignal Svj. If No, that is, if it is determined that the video signal Svdoes not jitter, the procedure then goes to a next step #400.

In step #400, a jitter confirmation subroutine for confirming that thevideo signal Sv is changed in state from not jittering (NO in step #300)to jittering is executed. That is, the jitter confirmation subroutine inthis step serves to confirm that the video signal Sv is, in fact, thejitter signal Svj. The jitter confirmation subroutine is executed by thejitter detector 22, and will be described in detail below with referenceto FIG. 5. The procedure then returns to the above step #200, whereinthe vertical average period calculation subroutine is executed.

On the other hand, if Yes in step #300, that is, if it is confirmed thatthe video signal Sv is the jitter signal Svj, the procedure goes to step#500.

In step #500, a non-jitter confirmation subroutine for confirming thatthe video signal Sv is changed in state from jittering (Yes in step#300) to non-jittering is executed. That is, the non-jitter confirmationsubroutine in this step serves to monitor the video signal Sv onceconfirmed as the jitter signal Svj in the jitter confirmation subroutine#400 to know any change to the non-jitter signal Svjn, and to confirm asit is. The non-jitter confirmation subroutine is executed by the jitterdetector 22, and will be described in detail below with reference toFIG. 6. The procedure then goes to a next step #800.

In step #800, based on the jitter amount signal Sdsp supplied by thejitter amount measuring unit 23 and the jitter transition signal Sffoutputted from the jitter detector 22, the appropriate adjustment amountof image quality correction for adjusting the predetermined amount ofcorrection SCAc based on the state of jitter of the inputted videosignal Sv. The adjustment amount of image quality correction calculationsubroutine in this step is executed by the image quality correctionamount calculator 24, and will be described in detail below withreference to FIG. 8. The procedure then goes to a next step #900.

In step #900, the amount of image quality correction to be applied tothe video signal Sv is calculated. The image quality correction amountcalculation amount subroutine in this step is executed by the imagequality correction amount calculator 24, and will be described in detailbelow with reference to FIG. 3. The procedure then goes to a next step#1000.

In step #1000, the predetermined amount of correction SCAc read from theROM 16 is adjusted to become the amount of image quality correctioncalculated in step #900, and the appropriate amount of correction SCAvis generated. The appropriate amount of correction SCAv is composed ofthe appropriate amount of noise reduction SNRv, the appropriatecorrection amount of horizontal edge enhancement SOEv, and theappropriate correction amount of scan speed SVMv. The procedure thenreturns to the above step #200.

<#200>

With reference to FIG. 4, the vertical average period calculationsubroutine in the above step #200 is described below.

In the initialization process in step #100 the field v is set to 0, theamount of jitter dsp is to 0, the jitter confirmation flag ex_jitter isto 0, and first_flag is to 1. After that, in step S201, it is determinedwhether the field v is 0 or not. If Yes, the procedure goes to stepS202.

In step S202, a stored vertical period Stf_sum, which is a variableindicating a value obtained by accumulating the vertical period Stf(v)of each field is set to 0, because this is the first time to calculatethe first vertical average period for the video signal (Yes in stepS201). The procedure then goes to step S204.

On the other hand, if No in step S201, that is, if the vertical averageperiod is calculated for a second or thereafter field of the videosignal Sv, the procedure skips the above step S202, and goes to stepS204.

In step S204, it is determined whether or not the field v is smallerthan loop having a predetermined value. If Yes, that is, if determinedsmaller, the procedure goes to step S206.

In step S206, the vertical period Stf(v) of the present field isobtained. The procedure goes to a next step S208.

In step S208, a variable Stf_sum is incremented by the vertical periodStf(v) obtained in step S206. Then, the procedure ends this subroutine.

On the other hand, if No in step S204, that is, if the field v is equalto loop, the procedure goes to step S212.

In step S212, the Stf_sum, which indicates accumulated vertical periodsStf(v) for the fields v corresponding to loop, is divided by loop forcalculating the average Stf_ave. Then, the procedure ends thissubroutine, and goes to the jitter amount calculation subroutine in step#700.

<#700>

With reference to FIG. 7, the jitter amount calculation subroutine inthe above step #700 is next described. The average vertical periodStf_ave is calculated in the jitter amount calculation subroutine of theabove step #200, and then the subroutine in the present step isexecuted.

In step S704, it is determined whether the field v is 0 or not. If No,that is, if the field v is not the first field of the video signal Sv tobe adjusted as to image quality correction, the procedure goes to stepS708.

In step S708, a variable Stf_buff for calculating the vertical periodStf(v) is set to 0. The procedure then goes to step S710.

On the other hand, if Yes in step S704, that is, if the field v is thefirst field of the video signal Sv to be adjusted as to image qualitycorrection, the procedure goes to step S710.

In step S710, the vertical period Stf(v) of the present field isobtained. The procedure then goes to step S712.

In step S712, it is determined whether the field v is smaller than loopor not. If Yes, that is, if the field v has a value smaller than loop,the procedure goes to step S614.

In step. S714, the variable Stf_buff is incremented by(Stf(j)−Stf_ave)². The procedure then goes to a next step S716.

In step S716, the field v is incremented by 1. The procedure then endsthe subroutine, and goes to step #300.

On the other hand, if No in step S712, that is, if it is determined thatthe field v is equal to loop, the procedure goes to step S718.

In step S718, Stf_buff^(½) is set to the amount of jitter dsp. Theprocedure then goes to a next step S720.

In step S720, the field v is set to 0. The procedure then ends thesubroutine, and goes to step #300.

<#400>

With reference to FIG. 5, the jitter confirmation subroutine in step#400 is next described. No is determined in the above step #300, thatis, the video signal Sv is the non-jitter signal, and then the procedurestarts this subroutine.

First, in step S402, the vertical period Stf(v) of the present field isobtained. The procedure then goes to a next step S404.

In step S404, the vertical period of the previous field Stf(v−1) issubtracted from the vertical period of the present field Stf(v) forcalculating an inter-field time difference tmp, which is a variableindicating the vertical period difference between successive two fields.The procedure then goes to a next step S406.

In step S406, it is determined whether an absolute value abs(tmp) of thein-field time difference tmp is larger than 1 or not. Note that, basedon the fact that the absolute value abs (tmp) of the in-field timedifference tmp of the jitter signal tends to become larger then 1, it isdetermined whether the video signal Sv jitters or not. If Yes, that is,if the video signal Sv is the jitter signal, the procedure goes to stepS408.

In step S408, a jitter judge counter Cej is incremented by 1. Theprocedure then goes to a next step S410. Note that, even though thevideo signal Sv is the jitter signal, due to various factors intransmission paths and devices, larger absolute value abs (tmp) of thein-field time differences tmp may be temporarily detected, and it may beerroneously judged in step S406 that the signal jitters. In order toprevent such erroneous judgment, the jitter judge counter Cej isprovided to detect the number of times of jitter signal judgment by stepS406.

In step S410, it is determined whether the jitter judge counter Cejrepresents a value equal to a jitter confirmation reference number oftimes Tej . The jitter confirmation reference number of times Tej is athreshold for confirming that the video signal Sv is the jitter signalSvj only after it has been successively judged a predetermined number oftimes that the signal jitters, thereby preventing erroneous judgment instep S406. That is, it is confirmed that the video signal Sv is thejitter signal Svj only after it has been successively judged the jitterconfirmation reference number of times Tej in step S406 that the signaljitters. The jitter confirmation reference number of times Tej can beset to an arbitrary value of 3 or more. As the jitter confirmationreference number of times Tej is larger, confirmation accuracy isimproved more. Normally, 5 is enough to ensure confirmation accuracy atpractical level. In this step, if No, that is, if it is not confirmedthat the video signal Sv is the jitter signal Svj, the procedure endsthe subroutine, and returns to #200.

On the other hand, if Yes in the present step S410, that is, if it isconfirmed that the video signal is the jitter signal, the procedure goesto step S412.

In step S412, the jitter confirmation flag ex_jitter is set to 1. Theprocedure then ends the present subroutine, and returns to the abovestep #200.

If No in the above step S406, that is, if it is confirmed that the videosignal Sv does not jitter, the procedure goes to step S414.

In step S414, the judge counter Cej is set to 0. The procedure then endsthe present subroutine, and returns to the above step #200.

The operation of the present subroutine has been described above by eachstep, and will be specifically described below based on the state of thevideo signal Sv.

When the correction adjuster CA is initiated, the video signal Sv isconfirmed to be the non-jitter signal (#100). Therefore, the proceduregoes to steps #200, #300, and then step #400. After steps S402 and S404,it is judged in step S406 whether the video signal Sv jitters.

If judged as the jitter signal, the procedure goes to steps S408, S410,#200, #300, and then S402 to S408, and it is judged in step S410 thatthe signal is the jitter signal Svj . After that, in step S412, thejitter confirmation flag ex_jitter is set to 1, and the procedure thenreturns to step #200. After step #200, it is judged in step #300 as Yes,that is, it is judged that the jitter confirmation flag ex_jitter=1, theprocedure goes to step #500.

<#500>

With reference to FIG. 6, the non-jitter confirmation subroutine in theabove step #500 is next described. After Yes in the above step #300,that is, after the jitter signal SVj is confirmed by the jitterconfirmation subroutine of step #400, the subroutine of the present stepstarts to be executed.

In step S502, it is determined whether the video signal Sv supplied tothe image quality correction device IQCp is interrupted or not. It isdetermined that the video signal Sv is interrupted if the horizontalsynchronization signal Hsync or the vertical synchronization signalVsync is not supplied or if the video signal Sv is switched to anothervideo signal by a video signal switch button cooperatively provided tothe image quality correction device IQCp. If No, that is, if it isdetermined that the video signal Sv is continuously supplied, theprocedure goes to step S504.

In step S504, the vertical period Stf(v) is obtained. The procedure thengoes to a next step S506.

In step S506, the in-field time difference tmp is calculated. Theprocedure then goes to a next step S508.

In step S508, it is determined whether or not the absolute value abs(tmp) of the in-field time difference tmp is 1 or less. If Yes, that is,if it is judged that the video signal is the non-jitter signal, theprocedure goes to step S510.

In step S510, the non-jitter judge counter Cnj is incremented by 1. Theprocedure then goes to a next step S512.

Note that, even if the video signal Sv is the jitter signal, due tovarious factors in transmission paths and devices, a smaller absolutevalue absolute value abs(tmp) of the in-field time difference tmp may betemporarily detected, and it may be erroneously judged in step S508 thatthe signal does not jitter. In order to prevent such erroneous judgment,the non-jitter judge counter Cnj is provided to detect the number oftimes of non-jitter signal judgment by step S508.

Instep S512, it is determined whether the non-jitter judge counter Cnjrepresents a value equal to a non-jitter confirmation reference numberof times Tnj. The non-jitter confirmation reference number of times Tnjis a threshold for confirming that the video signal Sv is the non-jittersignal Svjn only after it has been successively judged a predeterminednumber of times that the signal is the non-jitter signal, therebypreventing erroneous judgment in step 510. The non-jitter confirmationreference number of times Tnj can be set to an arbitrary value of 3 ormore. As the non-jitter confirmation reference number of times Tnj islarger, confirmation accuracy is improved more. Normally, 5 is enough toensure confirmation accuracy at practical level.

If No in this step, that is, if it is not confirmed that the videosignal Sv is the non-jitter signal, the procedure ends the presentsubroutine. On the other hand, if Yes in this step, that is, if it isconfirmed that the video signal Sv is the non-jitter signal Svjn, theprocedure goes to step S514.

In step S514, the jitter confirmation flag ex_jitter is set to 0, andfirst_flag is set to 1. The procedure then ends the present subroutine,and goes to the image quality correction adjustment amount calculationsubroutine of #800.

If Yes in the above step S502, that is, if it is determined that thevideo signal Sv is interrupted, the procedure skips the above steps S504to S510, and goes to step S514. This is because if the video signal Svis interrupted, image quality correction, which is the object of thepresent invention, is not required itself.

Furthermore, if No in step S508, that is, if it is judged that the videosignal Sv is the jitter signal, the procedure goes to a next step S516.

In step S516, the non-jitter judge counter Cnj is set to 0, and then theprocedure ends the present subroutine. The procedure then goes to theabove-stated image quality correction adjustment calculation subroutineof step #800.

The operation of the present subroutine has been described by each step,and will be specifically described below based on the state of the videosignal Sv. After the above steps #100 to #400, as to the video signalconfirmed as the jitter signal Svj, it is judged in step S508 aftersteps S502, S504, and S506 whether jitter in the video signal Sv has notbeen solved, that is, whether the video signal is the non-jitter signal.

If judged as the non-jitter signal, the procedure goes to step S510.Then, if, in step S512, the non-jitter judgment number of times Cnj doesnot reach the non-jitter confirmation reference number of times Tnj, theprocedure goes to the non-jitter confirmation subroutine of step #800with the jitter confirmation flag ex_jitter=1. The procedure then goesto steps #500, #800, #900, #1000, #200, #700, and #300, and then returnsto step #500. Then, after it is determined that the jitter signal Svj ischanged to the non-jitter signal Svjn (Yes in step S512), the jitterconfirmation flag ex_jitter=0 and first_flag=1 (step S514) in step S514and, with that, the procedure goes to step #800.

<#800>

With reference to FIG. 8, the image quality correction adjustment amountcalculation subroutine in the above step #800 is next described. Afterthe jitter state of the video signal Sv is detected through thenon-jitter confirmation subroutine of #500, the following procedure isexecuted.

In step S802, it is determined whether the jitter confirmation flagex_jitter is 0. If Yes, that is, if the video signal has been identifiedin #500 as the non-jitter signal Svjn, the procedure goes to step S804.

In step S804, the amount of jitter dsp found in step #700 (S718) isobtained. The procedure then goes to step S806.

In step S806, it is determined whether first_flag is 0. If Yes, that is,if the present video signal Sv is changed from the jitter signal Svj tothe non-jitter signal Svjn and also is continuously subjected to imagequality correction adjustment processing, the procedure goes to stepS807.

In step S807, the amount of jitter dsp is subtracted from the amount ofjitter of the previous field dsp_buff to calculate the in-field jitteramount difference Δdsp. The procedure then goes to step S808.

In step S808, it is determined whether the in-field jitter amountdifference is larger than 0. If Yes, that is, if the amount of jitter isregarded as becoming larger, the procedure goes to step S810.

In step S810, an adjustment variable x for adjusting the amount of imagequality correction is incremented by 1. The procedure then goes to anext step S811. This process is to match the present adjustment to achange of jitter in the video signal Sv. In other words, since jitter ofthe video signal Sv increases compared with that in the previous field,it is determined that a present adjustment amount of image qualitycorrection y is not appropriate (insufficient adjustment), and theadjustment variable x is incremented for enhancing the adjustment. Then,the procedure goes to step S811.

In step S811, dsp_buff is set as the amount of jitter of the presentfield dsp. The procedure then goes to step S811.

In step S812, a value f(x+1) defined as a function of the adjustmentvariable x+1 is taken as the adjustment amount of image qualitycorrection y. That is, the predetermined amount of correction read fromthe ROM 16 is adjusted with f(x+1), and the result is outputted as theappropriate amount of correction SCAv. The procedure then ends thepresent subroutine, and goes to step #900.

Note that, if No in the above step S808, that is, if the amount ofjitter in the present field is regarded as not becoming larger than thatin the previous field, the procedure goes to step S814.

In step S814, it is determined whether the in-field jitter amountdifference Δdsp is 0. If yes, that is, if the amount of jitter isregarded as not changing between fields, the procedure goes to the abovestep S811.

In step S812, the value f(x) defined by the present correction variablex is taken as the adjustment amount of image quality correction y. Thatis, the predetermined amount of correction SCAc read from the ROM 16 isadjusted with the value f(x), and the result is outputted as theappropriate amount of correction SCAv.

Note that, if No in step S814, that is, if jitter of the video signal Svdemonstrates a decreasing tendency, the procedure goes to step S816.

In step S816, the adjustment variable x is decremented by 1. Theprocedure then goes to step S811. This is because, since jitter of thevideo signal Sv decreases compared with that in the previous field, itis determined that the present adjustment amount of image qualitycorrection y is not appropriate (excessive adjustment), and theadjustment variable x is decremented for lessening the adjustment.

In step S812, a value f(x−1) defined as a function of the adjustmentvariable x−1 is taken as the adjustment amount of image qualitycorrection y. That is, the predetermined amount of correction read fromthe ROM 16 is adjusted with f(x−1), and the result is outputted as theappropriate amount of correction SCAv.

On the other hand, if No in the above step S806, that is, if it isconfirmed that the video signal Sv is changed from the non-jitter signalSvjn to the jitter signal Svj and correction adjustment is firststarted, the procedure goes to step S818.

In step S818, the adjustment variable x is set as the amount of jitterdsp, and first_flag is set to 0. The reason for this is as follows:first_flag is not 0 (step S806) and, therefore, when correctionadjustment is first applied to the video signal Sv, the adjustmentvariable x as a reference is provided with the amount of jitter dsp atthat moment, thereby appropriately setting, for the first time, theadjustment amount of image quality correction y. As such, first_flag isreset to 0, and thereafter the adjustment variable x defined by theamount of jitter dsp is taken as a reference for adjusting theadjustment amount of image quality correction y (S810, S816, and S812).

Furthermore, if No in the above step S802, that is, if it is confirmedthat the video signal Sv is the non-jitter, the procedure goes to stepS820.

In step S820, the adjustment amount of image quality correction is setto 1. In other words, the value of the predetermined amount ofcorrection SCAc read from the ROM 16 is outputted, as it is, as theappropriate amount of correction SCAv.

Next, with reference to FIGS. 11 and 12, methods of adjusting imagequality correction are specifically described. There are two maincategories for image quality correction. A first one includesenhancement of a portion varied in luminance (edge) to sharpen thereproduced image, such as edge correction and speed modulation. A secondone includes removal of a portion slightly varied in luminance or randomhigh-frequency components to stabilize the reproduced image, such as NR(noise reduction) and coring.

Image quality correction processes make the reproduced image better.When the video signal jitters, however, these correction processes donot improve but worsen the image quality if applied uniformly as is thecase of the signal that is not jittering. Thus, in the presentembodiment, it is determined whether the video signal Sv jitters, thatis, whether between the jitter signal Svj or the non-jitter signal Svjn.Based on the determination result, the amount of image qualitycorrection is automatically adjusted (controlled).

However, determination of the image quality may greatly vary dependingon viewers. Therefore, in order to enable viewers to adjust (control)the image quality, the following two methods are provided as shown inFIGS. 11 and 12. In each drawing, the vertical axis represents theamount of image quality correction SCA; the horizontal axis representsthe absolute value of the amount of jitter as the basis of adjustment(control) by a viewer; a solid line represents the amount of imagequality correction SCA (SNR, SOE, and SVM); a dotted line represents theappropriate correction amount of noise reduction SNRv, and analternate-dashed-and-dotted line represents the appropriate correctionamount of horizontal edge enhancement SOEv and the appropriatecorrection amount of scan speed SVMv.

Exemplarily illustrated in FIG. 11 is a method of adjusting, accordingto the amount of jitter, slopes of predetermined amounts of correctionSCAc (SNRc, SOEc, and SVMc), which are basic amounts for image qualitycorrection. The appropriate correction amount of noise reduction SNRv(the dotted line) is obtained by adjusting the correction amount ofnoise reduction SNRc to the positive side according to the amount ofnoise. On the other hand, the appropriate correction amount ofhorizontal edge enhancement SOEv and the appropriate correction amountof scan speed SVMv are obtained by adjusting the correction amount ofhorizontal edge enhancement SOEc and the correction amount of scan speedSVMc, respectively, to the negative side according to the amount ofnoise. In this case, the adjusted slope can be further adjusted by theviewer to his/her taste.

Exemplarily illustrated in FIG. 12 is a method of uniformly increasingor decreasing the predetermined amounts of correction SCAc (SNRc, SOEc,and SVMc), which are the basic amounts for image quality correction, foradjustment. In a similar manner to that illustrated in FIG. 11, theappropriate correction amount of noise reduction SNRv (the dotted line)is adjusted in the positive side based on the amount of noise. On theother hand, the appropriate correction amount of horizontal edgeenhancement SOEv and the appropriate correction amount of scan speedSVMv are adjusted in the negative side according to the amount of noise.In this case, the uniformly adjusted amount can be further increased ordecreased for adjustment by the viewer to his/her taste.

<#900>

With reference to FIG. 13, a concept of an image quality correctionamount calculation subroutine of step #900 is described. In the drawing,the vertical axis represents the amount of image quality correctiony=f(x) and the horizontal axis represents the amount of jitter dsp. Asolid line represents a relation between the amount of jitter dsp andthe amount of image quality correction f(x), but this line is notnecessarily solid, but may be a curve defined by a predeterminedcurvature. Exemplarily illustrated in the drawing is the method ofadjusting the slope with respect to the basic amount of correction shownin FIG. 13.

<#1000>

With reference to FIG. 14, a concept of an image quality correctionparameter generation subroutine of step #1000 is described. In thedrawing, the vertical axis represents the amount of image qualitycorrection SCA (SNR, SOE, and SVM); the horizontal axis represents theamount of jitter dsp; a dotted line represents the appropriatecorrection amount of noise reduction SNRv; and analternate-dotted-and-dashed line represents the appropriate correctionamount of horizontal edge enhancement SOEv and the appropriatecorrection amount of scan speed SVMv.

As described above, the appropriate correction amount of noise reductionSNRv is adjusted in the positive side according to jitter, andcalculated by multiplying the correction amount of noise reduction SNRcby the adjustment amount of image quality correction y=f(x). Theappropriate correction amount of horizontal edge enhancement SOEv andthe appropriate correction amount of scan speed SVMv are both adjustedin the negative side according to jitter, and calculated by multiplyingthe correction amount of horizontal edge enhancement SOEc and thecorrection amount of scan speed SVMc by the adjustment amount of imagequality correction y=f(x), respectively.

With reference to FIGS. 15 through 21, one exemplary modification of thecorrection adjuster CA according to the embodiment of the presentinvention is described below. The correction adjuster CA according tothe present embodiment is the same in structure as that shown in FIG. 2,but different in operation.

First, with reference to a main flow chart shown in FIG. 15, the mainoperation of the correction adjuster CA according to the presentexemplary modification is described. In the present exemplarymodification, the vertical average period subroutine of step #200, thejitter amount calculation subroutine of step #700, and the image qualitycorrection adjustment amount calculation subroutine of step #800 aremainly achieved in a simplified manner. Therefore, as shown in FIG. 15,steps #100, #200, #400, #500 and #900 shown in FIG. 3 are replaced by#100R, S206, #400R, #500R, and #900R, respectively, in the presentexemplary modification. Also in the present exemplary modification, #700in the embodiment is deleted.

Furthermore, the image quality adjustment amount calculation subroutineof step #800 and the image quality correction amount calculationsubroutine of step #900 in the embodiment are replaced by an imagequality adjustment amount calculation/image quality correction amountcalculation subroutine of step #1100.

With reference to FIG. 15, the main operation of the correction adjusterCA according to the present exemplary modification is briefly describedbelow and then, with reference to FIGS. 11, 12, and 13, the operation ineach step is described.

When the television set equipped with the image quality correctiondevice IQCp is started to operate, in step #100R, the correctionadjuster CA is first initialized. In other word, the jitter confirmationflag ex_jitter is set to 0; first_flag is set to 1; the field v is setto 0; and the adjustment amount of image quality correction y is set to0.

in step #100R, the correction adjuster CA is first initialized. In otherword, the jitter confirmation flag ex_jitter is set to 0; first_flag isset to 1; the field v is set to 0; and the adjustment amount of imagequality correction y is set to 0.

As such, in a similar manner to that in the embodiment, when the imagequality correction device IQCp (correction adjuster CA) is started tooperate, the video signal Sv is regarded as not jittering, and alsoimage quality correction adjustment is regarded as not having beenstarted. However; the predetermined amount of correction SCAc read fromthe ROM 16 is set, as it is, as the appropriate amount of correctionSCAv (the adjustment amount of image quality correction y=1). Theprocedure then goes to a next step S206.

In step S206, similarly in the above described S206, the vertical periodStf(v) is obtained. Then, if it is determined in step #300 that it isnot confirmed that the video signal Sv is the jitter signal Svj, theprocedure goes to a next step #400R. If confirmed as the jitter signalSvj, the procedure goes to step #500R.

A detailed flow chart of step #400R is shown in FIG. 16. The subroutinein the present embodiment is similar to the jitter confirmationsubroutine already described in the above embodiment with reference toFIG. 5 except that step S402 for obtaining the vertical period Stf(v) isdeleted. Therefore, description is omitted herein.

A detailed flow chart of step #500R is shown in FIG. 17. The subroutinein the present embodiment is similar to the non-jitter confirmationsubroutine already described in the above embodiment with reference toFIG. 6 except that step S504 for obtaining the vertical period Stf(v) isdeleted. Therefore, description is omitted herein.

<#1100>.

With reference to FIGS. 20 and 21, the concept of processing in thejitter amount calculation/image quality correction adjustment amountcalculation subroutine in step #1100 is described below.

This processing is suggested as an alternative measure, becausecalculation of the amount of jitter dsp and the amount of correctionincreases a load on a computer according to the above embodiment of thepresent invention. In each drawing, the vertical axis representsfrequencies, while the horizontal axis represents stacks. A stack (stk)indicates a vertical period difference (difference in the number of CLK)ΔTf between the previous field (v−1) and the present field (v), but maybe the in-field vertical period difference ΔStf(v)

In the present example, eight stacks are provided whose in-field perioddifferences ΔTf are 0−1, 2−4, 5−7, 8−10, 11−13, 14−16, 17−19, and 20 ormore, respectively. The number of stacks Stk and the in-field perioddifference ΔTfg are determined as appropriate in consideration ofeffects of correction adjustment. Each stack Stk is given a stack number(Stk No.) as 1, 2, 3, 4, 5, 6, 7, and 8, based on each in-field perioddifference ΔTfg. Hereinafter, each stack is identified as stk(k), wherek is a variable representing the stack number.

In the present exemplary modification, the jitter amountcalculation/image quality correction adjustment amount calculation iscarried out through the following steps. First, the stacks Stk(k) isprovided as many as the level to which the predetermined amount ofcorrection SCAc is desired to be changed.

Then, the stack Stk(k) that corresponds to the value of the in-fieldperiod difference ΔTfg accumulates the frequency of appearance of thatvalue, and a histogram of the amount of jitter is obtained. Among thestacks having more frequencies of appearance than a threshold th_A for nfields, the one having the largest in-field period difference ΔTfg isselected, and given a correction value from a ROM table. Note that tosmooth the correction result, the stack Stk and the adjustment value areset appropriately.

With reference to FIG. 21 for describing the above, stacks having morefrequencies of appearance than the threshold th_A are Stk(4), Stk(5),and Stk(7). Of these three stacks Stk, Stk (7) has the largest inin-field period difference ΔTf, and therefore, the correction value toStk(7) is read from the ROM table.

With reference to FIGS. 18 and 19, the jitter amount calculation/imagecorrection adjustment amount calculation subroutine of #1100 isdescribed.

First, in step S2, it is determined whether the field v is 0 or not. IfYes, that is, if it is the first field for the video signal Sv, theprocedure goes to step S4.

In step S4, a variable k representing the stack number is set to 0. Theprocedure then goes to step S6.

In step S6, k is incremented by 1. The procedure then goes to step S8.

In step S8, stk(k) is set to 0. The procedure then goes to step S10.

In step S10, it is determined whether k is smaller than n or not. IfYes, the procedure returns to steps S6 and then S8. The procedurerepeats a loop process of steps S6, S8, S10 until it is determined k=n.If No in this step, on the other hand, the procedure exits from theabove loop to a next step S12.

On the other hand, if No in step S2, that is, if it is determined thatthe video signal Sv has been continuously processed, the procedure skipsthe above steps S4 to S10, and goes to step S12.

In step S12, it is determined whether the field v is smaller than theloop or not. If Yes, the procedure goes to step S14.

In step S14, the vertical period of the previous field Stf(v−1) issubtracted from the vertical period of the present field Stf(v), and theresult is set as dif. dif corresponds to the in-field period differenceΔTf shown in FIGS. 20 and 21. The procedure then goes to step S16.

In step S16, it is determined whether dif is not less than 0 and issmaller than th(0). If Yes, the procedure goes to step S18.

In step S18, stk(0) is incremented by 1. By repeating this step, thefrequency in the stack stk(0) can be calculated. The procedure then goesto step S30.

If No in step S20, on the other hand, the procedure goes to step S24,wherein the frequency in a stack Stk(n−1) is to be found.

In step S20, it is determined whether dif is not less than th(0) and issmaller than th(1). If Yes, the procedure goes to step S22.

In step S22, stk(1) is incremented by 1. By repeating this step, thefrequency in the stack Stk(1) can be calculated. The procedure then goesto step S30.

If No in step S20, on the other hand, the procedure toes to step S24,wherein the frequency in a stack Stk(n−1) is to be found.

In step S24, it is determined whether dif is smaller than th(n−1). IfYes, the procedure goes to step 526. If Yes, the procedure goes to stepS26.

In step S26, stk(n−1) is incremented by 1. The procedure then goes tostep S30.

If No in step S24, on the other hand, the procedure goes to step S28,wherein the frequency in a next stack Stk(n) is to be found.

In step S28, stk(n) is incremented by 1. The procedure then goes to stepS30. Note that a case where n is 4 is shown in FIG. 18 as space permits.As described above, however, n maybe an arbitrary number appropriatelydetermined for obtaining effects of smoother correction adjustment. Notethat, after steps S18, S22, S26, and S28, a histogram of the jitteramount can be obtained.

Furthermore, if No in the above step S12, that is, if it is determinedthat v is equal to loop, the procedure goes to step S32.

In step S32, it is determined whether the jitter confirmation flagex_jitter is 0 or not. If No, that is, if it is confirmed that the videosignal Sv is the jitter signal Svj, the procedure goes to step S34.

In step S34, adj_tem is set to 0. The procedure then goes to a next stepS36.

In step S36, k is set to 0. The procedure then goes to a next step S38.

In step S38, it is determined whether k is smaller than n. If Yes, theprocedure goes to step S40.

In step S40, it is determined whether stk(k)≧th_A. If No, the proceduregoes to step S42.

In step S42, adj_temp is set to k. The procedure then goes to step S44.

In step S44, k is incremented by 1. The procedure returns to step S38.

If Yes in step S40, on the other hand, the procedure skips step S42, andgoes to step S44.

If No in step S38, that is, if k=n, the procedure goes to step S46.

In step S46, it is determined whether first_flag is 1 or not. If No, theprocedure goes to step S48.

In step S48, it is determined whether a value obtained by subtractingthe adjustment variable x from adj_tem is larger than 0. If Yes, theprocedure goes to step S50.

In step S50, the adjustment variable x is incremented by 1. Theprocedure then goes to step S58.

In step S58, Sadj(x) is set as y. The procedure then goes to step S62.

In step S62, the field v is set to 0. The procedure ends the presentsubroutine.

If No in step S48, on the other hand, the procedure goes to step S52. Instep S52, it is determined whether adj_tmp is equal to the adjustmentvariable x. If Yes, the procedure goes to step S54.

In step S54, the adjustment variable x is decremented by 1. Theprocedure then goes to step S58.

If No in step S46, the procedure goes to step S56.

In step S56, the value of the adjustment variable x is set as adj_tmp,and first_flag is set to 0. The procedure then goes to step S58.

On the other hand, if Yes in step S32, that is, if it has been confirmedthat the video signal Sv is the non-jitter signal Svjn, the proceduregoes to step S60.

Then, based on the adjustment amount of image quality correction ycalculated in the present subroutine, image quality correctionadjustment is carried out in steps #90OR and #1000 as described above.Note that step #90OR is basically the same as the above step #900.

As such, according to the present invention, a video signal includingjitter components is automatically detected, and the amount of jitter ismeasured. According to the amount, the amount of horizontal edgecorrection, the amount of speed modulation, and the amount of noisereduction is adaptively increased or decreased. Thus, it is possible tostructure a broadcast receiving device that corrects optimal imagequality according to the state of an input signal.

INDUSTRIAL APPLICABILITY

As such, the present invention can be utilized for such purpose asachieved in television, that is, for reproducing and displaying an imagefrom a video signal.

What is claimed is:
 1. A jitter detection device for detecting jitter ina video signal, said device comprising: a vertical period measuringmeans for measuring a vertical period for one field of the video signaland generating a vertical period signal; a jitter determination meansfor determining, based on the vertical period signal, whether the videosignal jitters or not, and generating a jitter determination signal; ajitter determination counting means for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal jitters, and generating a jitter determinationcounter signal; a jitter confirmation means for confirming, based on thejitter determination counter signal, that the video signal is a jittersignal if it is determined a first predetermined number of times thatthe video signal jitters; a non-jitter counting means for counting,based on the jitter determination signal, the number of times it issuccessively determined that the video signal does not jitter, andgenerating a non-jitter determination counter signal; a non-jitterconfirmation means for confirming, based on the non-jitter determinationcounter signal, that the video signal is a non-jitter signal if it isdetermined a second predetermined number of times that the video signaldoes not jitter.
 2. The jitter detection device according to claim 1,wherein said jitter determination means: determines that the videosignal jitters when an absolute value of a difference between a verticalperiod of a present field and a vertical period of a previous field islarger than 1; and determines that the video signal does not jitter whenthe absolute value is smaller than
 1. 3. The jitter detection deviceaccording to claim 1, further comprising a jitter amount calculatingmeans for sequentially calculating a dispersion value of verticalperiods.
 4. An image quality correction device for correcting quality ofan image reproduced based on a video signal according to an amount ofjitter in the video signal, said device comprising an image qualitycorrection adjusting means that comprises at least one of: a noisereducing means for reducing noise of the video signal based on apredetermined correction amount of noise reduction; a horizontal edgeenhancing means for enhancing a horizontal edge of the video signalbased on a predetermined correction amount of horizontal edgeenhancement; and a scan speed modulating means for enhancing a specificpart of the video signal based on a predetermined amount of scan speedmodulation; wherein, according to the amount of jitter, said imagequality correction device increases the correction amount of noisereduction by a predetermined adjustment value, decreases the correctionamount of horizontal edge enhancement by the adjustment value, anddecreases the amount of scan speed modulation by the adjustment value.5. The image quality correction device according to claim 4, furthercomprising a jitter detection device that comprises: a vertical periodmeasuring means for measuring a vertical period for one field of thevideo signal and generating a vertical period signal; a jitterdetermination means for determining, based on the vertical periodsignal, whether the video signal jitters or not, and generating a jitterdetermination signal; a jitter determination counting means forcounting, based on the jitter determination signal, the number of timesit is successively determined that the video signal jitters, andgenerating a jitter determination counter signal; a jitter confirmationmeans for confirming, based on the jitter determination counter signal,that the video signal is a jitter signal if it is determined a firstpredetermined number of times that the video signal jitters; anon-jitter counting means for counting, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal does not jitter, and generating a non-jitterdetermination counter signal; a non-jitter confirmation means forconfirming that the video signal is a non-jitter signal if it isdetermined, based on the non-jitter determination counter signal, asecond predetermined number of times that the video signal does notjitter.
 6. The image quality correction device according to claim 5,wherein said image quality correction adjusting means dynamicallyadjusts at least one of the correction amount of noise reduction, thecorrection amount of horizontal edge enhancement, and the amount of scanspeed modulation, while sequentially calculating a dispersion value ofvertical periods.
 7. The image quality correction device according toclaim 6, wherein said image quality correction adjusting means furthercomprises a histogram means for generating a histogram composed offrequencies of appearance as the amount of jitter, wherein: at least oneof the correction amount of noise reduction, the correction amount ofhorizontal edge enhancement, and the amount of scan speed modulation isadjusted by an amount of adjustment predetermined corresponding to theamount of jitter and the frequency of appearance that is larger than apredetermined threshold.
 8. The image quality correction deviceaccording to claim 4, wherein the amount of jitter in a present field isused as the adjustment value immediately after the video signal ischanged from a non-jitter signal to a jitter signal.
 9. The imagequality correction device according to claim 5, further comprising anadjustment suppressing means for suspending adjustment of at least oneof the correction amount of noise reduction, the correction amount ofhorizontal edge enhancement, and the amount of scan speed modulation ifthe video signal is changed from the jitter signal to the non-jittersignal.
 10. A jitter detection device for detecting jitter in a videosignal, said device comprising: a vertical period measuring unitoperable to measure a vertical period for one field of the video signaland generate a vertical period signal; a jitter determination unitoperable to determine, based on the vertical period signal, whether thevideo signal jitters or not, and generate a jitter determination signal;a jitter determination counter operable to count, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal jitters, and generate a jitter determinationcounter signal; a jitter confirmation unit operable to confirm, based onthe jitter determination counter signal, that the video signal is ajitter signal if it is determined a first predetermined number of timesthat the video signal jitters; a non-jitter counting unit operable tocount, based on the jitter determination signal, the number of times itis successively determined that the video signal does not jitter, andgenerate a non-jitter determination counter signal; a non-jitterconfirmation unit operable to confirm, based on the non-jitterdetermination counter signal, that the video signal is a non-jittersignal if it is determined a second predetermined number of times thatthe video signal does not jitter.
 11. The jitter detection deviceaccording to claim 10, said jitter determination unit is operable to:determine that the video signal jitters when an absolute value of adifference between a vertical period of a present field and a verticalperiod of a previous field is larger than 1; and determine that thevideo signal does not jitter when the absolute value is smaller than 1.12. The jitter detection device according to claim 10, furthercomprising a jitter amount calculator operable to sequentially calculatea dispersion value of vertical periods.
 13. An image quality correctiondevice for correcting quality of an image reproduced based on a videosignal according to an amount of jitter in the video signal, said devicecomprising an image quality correction adjuster that comprises at leastone of: a noise reduction unit operable to reduce noise of the videosignal based on a predetermined correction amount of noise reduction; ahorizontal edge enhancer operable to enhance a horizontal edge of thevideo signal based on a predetermined correction amount of horizontaledge enhancement; and a scan speed modulator operable to enhance aspecific part of the video signal based on a predetermined amount ofscan speed modulation; wherein, according to the amount of jitter, saidimage quality correction device is operable to increase the correctionamount of noise reduction by a predetermined adjustment value, decreasethe correction amount of horizontal edge enhancement by the adjustmentvalue, and decrease the amount of scan speed modulation by theadjustment value.
 14. The image quality correction device according toclaim 13, further comprising a jitter detection device that comprises: avertical period measuring unit operable to measure a vertical period forone field of the video signal and generate a vertical period signal; ajitter determination unit operable to determine, based on the verticalperiod signal, whether the video signal jitters or not, and generate ajitter determination signal; a jitter determination counter operable tocount, based on the jitter determination signal, the number of times itis successively determined that the video signal jitters, and generate ajitter determination counter signal; a jitter confirmation unit operableto confirm, based on the jitter determination counter signal, that thevideo signal is a jitter signal if it is determined a firstpredetermined number of times that the video signal jitters; anon-jitter counting unit operable to count, based on the jitterdetermination signal, the number of times it is successively determinedthat the video signal does not jitter, and generate a non-jitterdetermination counter signal; a non-jitter confirmation unit operable toconfirm that the video signal is a non-jitter signal if it isdetermined, based on the non-jitter determination counter signal, asecond predetermined number of times that the video signal does notjitter.
 15. The image quality correction device according to claim 14,wherein said image quality correction adjuster is operable todynamically adjust at least one of the correction amount of noisereduction, the correction amount of horizontal edge enhancement, and theamount of scan speed modulation, while sequentially calculating adispersion value of vertical periods.
 16. The image quality correctiondevice according to claim 15, wherein said image quality correctionadjuster further comprises a histogram unit operable to generate ahistogram composed of frequencies of appearance as the amount of jitter,wherein: at least one of the correction amount of noise reduction, thecorrection amount of horizontal edge enhancement, and the amount of scanspeed modulation is adjusted by an amount of adjustment predeterminedcorresponding to the amount of jitter and the frequency of appearancethat is larger than a predetermined threshold.
 17. The image qualitycorrection device according to claim 13, wherein the amount of jitter ina present field is used as the adjustment value immediately after thevideo signal is changed from a non-jitter signal to a jitter signal. 18.The image quality correction device according to claim 14, furthercomprising an adjustment suppressor operable to suspend adjustment of atleast one of the correction amount of noise reduction, the correctionamount of horizontal edge enhancement, and the amount of scan speedmodulation if the video signal is changed from the jitter signal to thenon-jitter signal.